The invention relates to a method of adjusting a roller in a rotary printing press.
The roller to be adjusted may for example be a printing cylinder or sleeve in a flexographic or gravure or offset printing press, or an anilox roller in a flexographic printing press. A parameter that will have to be adjusted for such a roller will be the force or pressure with which the peripheral surface of the roller is radially pressed against another member of the printing press, e.g. an impression cylinder or back pressure cylinder, if the roller to be adjusted is a printing cylinder, or a printing cylinder, if the roller to be adjusted is an anilox roller. This pressure parameter may be defined individually for the two opposite sides of the printing press which are called the drive side and the operating side. At least in case of a printing cylinder, parameters to be adjusted will typically also include the longitudinal register and the side register.
In a conventional printing press, the adjustment of these parameters is performed electronically by controlling suitable actuators or servo motors. Nevertheless, human intervention is still necessary for assessing the result of the adjustment operation by visually inspecting the printed image, and for entering commands to correct the settings. The adjustment operation is usually performed in a start-up phase of a print run, when a new roller or a new set of rollers has been mounted in the machine and the machine has been started to print images onto a web of a printing medium. As a result, a considerable amount of waste is produced until the adjustment operation has been accomplished and the quality of the printed images becomes satisfactory. In a modern high-speed printing press, the amount of waste that is produced in this way in the try-and-error type adjustment process may become as large as 600 m or more per print run. This implies not only a waste of web material but also a waste of time and hence a considerable reduction of the productivity of the printing press, especially when the print runs to be performed with a given set of rollers are relatively short.
Several attempts have been made to speed-up and automate the adjustment or setting of the rollers of a printing press in terms of longitudinal register, side register and also pressure. For example, EP 1 249 346 B1 describes a system and method for automated pressure setting, wherein the visual inspection of the printed images with the human eye is replaced by electronic image detection and feedback control of the pressure settings based on electronic image processing. Nevertheless, the adjustment procedure still requires a considerable amount of time and thus involves the production of waste.